SSH (Secure Shell) is a set of network protocols for securing connections between computers. In plain English, this means that you can use a utility on another device such as a PC to control your Pi, pretty much as if you were using the Pi’s Terminal directly.
Because your Pi has a default username and password, it could be targeted remotely by a
hacker, and for this reason, SSH is disabled by default. If you can connect your Pi to a monitor temporarily, you can enable SSH yourself.
First, open Terminal and run the following command:
Using your arrow keys, choose Option 5 (Interfacing Options), then select it by pressing Enter.
Next, choose Option P2 (SSH). Raspi-config will ask if you’re sure you want to enable.
Press Enter once again to confirm. You will see a confirmation message stating “The SSH
a server is enabled”.
If you do not have a monitor, don’t worry. Power off the Pi, remove its SD card, insert it into a card reader, and plug this into your computer. Find the /boot partition and create a file there named ssh.
You can use a text editor such as Microsoft’s Notepad or Apple’s TextEdit to do this but make sure that the file has no filename extension such as .txt. Safely eject the SD
card and reinsert into your Pi. SSH will now be enabled.
The next time you load the Pi with a monitor attached, you will see a warning that the default password for the Pi user has not been changed from “raspberry”.
To fix this, open Terminal and enter the following command:
sudo passwd pi
You’ll be asked to enter the new password twice. Note that this command itself can also be run over SSH.
Note:- I have written a post for people looking for the Best Monitor for Raspberry Pi to buy?, do read it If you are interested.